Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 231327

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
927 AM EDT Thu Mar 23 2017

High pressure will build across the area today, and move
offshore tonight. A warm front will cross the region Friday.
Low pressure may affect the area Sunday.


High pressure directly overhead this morning will shift offshore
by late today. This will allow for light and variable winds
this morning to gradually turn light southerly during the day
today. Otherwise, a mostly sunny day is in store with highs
about 10 degrees below climatological normals, in the mid 40s to
low 50s.


Tricky forecast tonight into early Friday. Skies may be clear
enough early this evening for radiational cooling to bring
temperatures back below freezing in many areas. Then, southerly
winds and increasing clouds look likely to start temps on the
upward trend after midnight, with many areas likely to return
back above freezing by morning. However, a warm front will also
be approaching from the west, and some rain is possible
especially closer to the Mason-Dixon line. Guidance is not in
great agreement, but the Canadian and European models do support
a period of light rain, while the NAM and GFS both are dry. With
temps possibly near or just below freezing at onset, a period of
freezing rain is possible overnight, most likely close to the
Mason-Dixon line and inland from the bay. Future shifts will
need to closely monitor this potential. Right now probability is
well below the 80% advisory criteria, so will just mention in
the HWO.

Otherwise, Friday will feature a significant warming as the warm
front crosses the area. Skies will feature plenty of clouds, but
southerly winds will become rather gusty, and temperatures
should warm through the 50s into the lower 60s in spots. Some
areas could even crack 70, but most places won`t just yet.
Southerly flow will continue Friday night, keeping it much
milder than the previous few nights. Saturday will remain
relatively cloudy, but enough breaks of sun are expected to
allow most places to soar into the 70s. This will be the first
widespread 70-degree day since March 9th. Records are in the
80s at DCA and BWI, but only 76 at IAD, so the latter is within

A backdoor cold front may try to drop back south on Saturday
night. Some guidance has backed off on this thought, which
would result in another mild night. Otherwise, an approaching
system may bring a few showers west, but generally dry weather


Low pressure currently over the Great Basin will slowly make
its way east across the country. The system is expected to be
cutoff and weakening/filling by the time it reaches the Midwest
Saturday night per 00Z ECMWF/GFS. Gulf moisture will stream
ahead of this system with rain over the area Sunday and Sunday
night. This looks to be a much better chance (likelies across
the CWA) for a soaking rain than the quick hitter mainly north
this Friday. Persistent warm/above normal conditions at least to
the middle of next week in continued southerly flow.


Expecting mainly VFR through Saturday night. Biggest concern
right now, concentrated mainly on MRB, is a chance of some light
freezing rain late tonight into early Friday. It will be a race
of warmer air moving in at the surface versus precip (if there
is some) moving in from the west. Further south and east, the
chance of precipitation is less and the chance of temps warming
up before it arrives is greater.

Winds will become southerly and a bit gusty (20-25 knots) on
Friday, and remain gusty as they swing more southwesterly

An occluded or warm front looks to cross the area Sunday into
Monday with likely rain/potential for MVFR conds across the area
in southerly flow.


Winds will gradually diminish over the bay this morning as high
pressure builds overhead with sub-SCA conditions. After that,
southerly flow up the bay should start to increase as a warm
front approaches, with SCA threat spreading up the bay overnight
and then to the adjacent waters during the day Friday. Winds
may diminish a bit overnight Friday but look likely to return to
SCA levels on Saturday with continued south to southwest flow.
With the water still rather chilly, mixing will reduce gusts a
bit over the water, but still expect 20 knots or so especially
near shore.

Sly flow prevails Sunday into next week. Sly/SEly channeling
into SCA levels possible at times through this time.


MARINE...Small Craft Advisory from 6 AM to 6 PM EDT Friday for ANZ530-
     Small Craft Advisory from noon to 6 PM EDT Friday for ANZ535-
     Small Craft Advisory from midnight tonight to 6 PM EDT Friday
     for ANZ532>534-540-541.


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